Mass spectrometry was originally dominated by massive instrumentation. Mass spectrometers would routinely fill an entire room and weigh hundreds, or even thousands of pounds. However, smaller and lighter instruments employing quadrupole technology eventually developed. Instrumentation built upon the “ion trap”, in which the entire mass spec analyzer could easily be held in the palm of one hand eventually developed.
Along with this compression in size, there were attempts made at developing portable mass spectrometers, allowing an operator the ability to essentially take the mass spectrometry lab to the sample, as opposed to taking the sample to the lab.
These small instruments faced numerous challenges. To start with, everything had to be powered by a portable battery. Additionally, a vacuum system needed to be developed that could handle the sample load, in addition to generating a workable vacuum for the instrument.
Various attempts have been made at producing small, portable, and even handheld mass spectrometers, with perhaps the most fundamental challenge being the creation of an appropriate vacuum, and the ability to maintain an acceptable working vacuum during operation of the instrument.
One approach taken by at least two organizations makes use of an ion pump. With this geometry, the mass spectrometer must initially be “pumped down” to a pressure, typically below 10−3 Torr. Once this pressure has been reached, the ion pump may be turned on and the instrument placed into service in the field. The ion pump must then be run either periodically, or at least intermittently, in order to maintain a workable operating pressure for the mass spectrometer. This geometry has the advantage that the ion pump has no moving parts and is very rugged for use in a field environment. The major drawback to the ion pump is that its operating life is inversely related to the pressure at which it operates. As the mass spectrometer is used to analyze samples, the pressure within the instrument increases, placing a larger load on the ion pump, directly reducing its lifetime. Further, the ion pump cannot simply be regenerated. The mass spectrometer must be opened up and the adsorbing material, typically a titanium strip, must be replaced.
Another approach taken by some developers has been to use a small turbomolecular pump, backed up by a correspondingly small roughing pump. This approach basically takes all the pumping hardware of a conventional lab mass spectrometer and places it into a portable mass spectrometer. Although this approach provides an ideal pumping system for a mass spectrometer, it has several severe drawbacks. The most significant being that the turbomolecular pump itself is a very delicate device and can be easily damaged through any type of sudden shock or sudden venting of the system.
Another attempt at developing a portable mass spectrometer has been to use a small cryocooling device in conjunction with a cold finger, but this approach required the use of an additional vacuum pump to pump down the mass spectrometer vacuum manifold prior to operating the cryocooler module.
Therefore, while mass spectrometers have seen dramatic reductions in size, their use in a demanding field environment still represents a major challenge.